Handling of one ship may be very different from another ship. Good knowledge of seamanship and experience increase the skill and competence of ship handler.
Factors affecting ship handling
- Means of propulsion
- Ships steering
- Shape of hull
- Disposition of superstructures
- Loading & trim
- Weather
- Depth & extent of water surrounding her
- Current or tidal stream
Forces affecting ship handling
- Propulsion machinery
- Rudder
- Anchor and chain cable
- Berthing hawsers
- Interaction forces
- Thugs
- Tidal stream/current
- Wind
Handling qualities of a particular ship depends on
- Number, size and type of propellers
- Horsepower and type of propelling machinery
Conventional propellers
There are two types of conventional propellers. They can be dived into two as fixed pitch propellers (FPP) and controlled pitch propellers (CPP). Conventional propellers rotate in the vertical or nearly vertical plane, and the direction of rotation can be Right-handed or Left-handed. A Right-handed propeller turns in a clockwise direction when viewed from aft, which means blade at the top of the cycle moves to the right, and a Left-handed propeller turns counter-clockwise which means top blade moving to left.
Specialized propulsion system
Some are some more types of specialized propellers available and some of them as follow.
- Bow Thrusters
- Voith Schneider (Vertical Axis or Cycloidal) propeller.
- Stern Azimuth Drive (Z Drive) and Azipod.
- Water Jet
Fixed pitch propellers
The blades and the boss of a Fixed Pitch Propeller (FPP) are made as one solid unit and the blades are set at a fixed angle. As it is not possible to alter the pitch of the blades, a FPP must rotate in the opposite direction when astern thrust is required. This requires a reversing gearbox or a separate astern turbine or electric motors that can put the shaft into reverse. The only way of increasing or decreasing the thrust of an FPP is by altering the speed of rotation. Single FPPs fitted to RN warships are all Right-handed. Twin FPPs in commonly turn outwards when going ahead; the port is left-handed and the starboard is right-handed. This ensures maximum lateral turning forces when turning at rest.
Controlled pitch propellers
To change a controlled pitch propeller (CPP) from propulsion ahead to propulsion astern, the blades are rotated in the hub from ahead-pitch to astern-pitch while the propeller continues to revolve in same direction. Changes in pitch are carried out by pumping actuating oil to the propeller hub through tubes inside the propeller shaft. Once the blades are set at maximum pitch, more thrust is obtained by increasing shaft revolutions with greater engine power. The single CPP fitted in the commonly Left-handed. Twin CPPs always turn inwards (ahead and astern); the port is right-handed and the starboard left-handed. This focusses the wake and increases the effectiveness of rudders. The lateral forces from astern propeller help a turn but are cancelled by the other propeller going ahead unless unbalanced power is used. The propeller is stopped by applying the Shaft Brake.
Types of propulsion machinery
- Steam turbines
- Diesel engines
- Gas turbines
- Electric engines